1. Field of the Invention
The present invention relates to an apparatus and a method for comparing drawings.
2. Description of the Related Art
With the development of IT technology and the digitized representation in daily life, the efficient management and retrieval of drawings are important problems to be solved. According to the statistical data, the number of drawings reached 3.5 billion at the start of 1990s in the USA and Canada only, and about 2,600 drawings are newly added every year. The annual cost of filing, copying, accessing, and preparing the drawings for distribution has exceeded one billion dollars. Recently, there are a number of individuals who have started studying methods of electronic management of drawings specifically by automatically generating and recognizing a DAC file from a drawing of a hard copy with a view to enhancing the efficiency and reducing the maintenance cost. Particularly in this method, a drawing similar to an inquiry drawing is automatically retrieved from a database. The retrieval of a drawing is performed by comparing the contents of drawings.
The comparison of drawings based on the contents brings about a valuable effect on applications. When an engineer designs a new type of product, it is common that many prior drawings are referred to. However, to search for related drawings, each document is to be searched. Therefore, it is a time and labor intensive technology. To solve the problem, a retrieving method has been proposed using text as ancillary means. That is, comment text is labeled in each drawing for use in retrieving a keyword. However, this method requires a laborious step in assigning text to a number of drawings, and text only cannot sufficiently represent the contents of the drawings. Therefore, this method may not output acceptable retrieval accuracy. If an automated comparison and retrieval technology can be developed, the efficiency of the operation of a designer can be remarkably improved with the designing and maintenance cost considerably reduced.
Recently, some individuals have been enthusiastically studying the comparison of drawings based on the contents, and have proposed a number of effective methods.
One of the disclosed methods is to compare the primitives of drawings proposed in the F-signature by S. Tabbone (refer to Nonpatent document 1). In this method, the drawings are retrieved after comparison with each other using the primitives taken from drawings, and no partial detection or comparison can be realized. Therefore, it is used in restricted applications.
Another disclosed method is to retrieve a drawing containing a characteristic portion using a combination of text and graphic structural information. Refer to Patent document 1. In this method, text is input for retrieval and compared with a geometric model stored in a model database, and finally a drawing is retrieved based on the shapes of the text and the model. Therefore, this method mainly depends on the retrieval mode of text, and mainly applied to the assemble engineering drawing.    [Nonpatent document 1] S. Tabbone, L. Wendling, K. Tombre, Matching of graphical symbols in line-drawing images using angular signature information, International Journal of Document Analysis and Recognition, volume 6, issue 1, Jun. 2003    [Patent document 1] U.S. Pat. No. 5,845,288
The conventional method of comparing drawings based on the contents of the drawings is insufficient as mentioned above, and a more complete drawing comparison apparatus or method based on the contents of drawings is demanded.